The present invention relates to a material having photocatalytic activity, more specifically, the present invention relates to a photocatalytic powder material having photocatalytic activity, a slurry containing the photocatalytic powder, an organic polymer composition containing the photocatalytic powder, a photocatalytic functional molded article of the organic polymer composition, a coating agent comprising the photocatalytic slurry, and a photocatalytic functional structure having provided on the surface thereof the polymer composition or the coating agent.
In recent years, photocatalytic fine particles using titanium dioxide are attracting attention as an environmental cleaning material for antimicrobial, deodorization, antifouling, air cleaning, water cleaning and the like. The photocatalytic mechanism of titanium dioxide is considered attributable to the following mechanism. Upon irradiation of light on a titanium dioxide fine particle, an electron and a hole are generated inside the titanium dioxide fine particle, which reacts with water or oxygen in the vicinity of the surface of a titanium dioxide fine particle to generate hydroxy radical or hydrogen peroxide. As a result, strong oxidation reduction activity of this hydroxy radical or hydrogen peroxide, harmful organic substances are decomposed into carbon dioxide and water, and thereby cleaned. Such photocatalytic activity of a titanium dioxide fine particle is thought to semipermanently continue as long as a titanium dioxide fine particle, light, water and oxygen are present.
By taking advantage of this photocatalytic property of titanium dioxide, as a representative application example, titanium dioxide fine particles are being kneaded into an easily handleable medium, such as fiber or a plastic molded article, or into a coating on the surface of a substrate, such as cloth or paper. However, decomposition or deterioration by the strong photocatalytic activity of titanium dioxide readily occurs not only on harmful organic materials or environmental pollutants but also on the medium itself such as fiber, plastic or paper and this is an obstacle to durability in practical use. Due to easy handleability of the titanium dioxide fine particle, a coating material comprising a mixture of titanium dioxide fine particles and a binder has been developed. However, an inexpensive binder having durability sufficiently high to overcome, for example, decomposition or deterioration on the medium has not yet been found.
JP-A-9-225319 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and JP-A-9-239277 disclose means for preventing and suppressing the deterioration of a resin medium or the deterioration of a binder due to the strong photocatalytic activity of titanium dioxide particles. The proposed means is a method of allowing a photo-inactive compound having such as aluminum, silicon and zirconium to be supported on a titanium dioxide particle in an archipelago shape having a steric barrier to retard the photocatalytic activity. According to this method, the photo-inactive compound is supported in an archipelago shape; however, specific sites of the resin medium or the binder disadvantageously remain present under the strong photocatalytic activity of titanium dioxide.
JP-A-10-244166 proposes a photocatalytic titanium dioxide obtained by coating a porous calcium phosphate on the surface of titanium dioxide. However, in this case, the photocatalytic activity disadvantageously decreases due to the coated calcium phosphate layer.
International Publication WO99/33566 discloses a powder material of titanium dioxide fine particles, where a porous coating layer of calcium phosphate is formed on at least a part of the surface of a titanium dioxide fine particle and an anionic surfactant is present at the interface therebetween.
With respect to a slurry containing titanium dioxide having photocatalytic activity, JP-A-10-142008 discloses an anatase-type titanium oxide-containing slurry which is obtained by heat-treating a titania sol, a titania gel form or a titania sol-gel mixture in a closed vessel simultaneously with a pressurization treatment and then dispersing using an ultrasonic wave or stirring the treated product.
JP-A-11-343426 discloses a photocatalytic coating material having excellent dispersion stability and specifically discloses a photocatalytic coating material containing, in a solvent, a silica sol and titanium oxide having a Raman spectrum peak in the range of 146 to 150 cmxe2x88x921 and being occupied by anatase type titanium dioxide in a ratio of 95% by mass or more.
Conventional techniques heretofore proposed cannot provide an industrially useful method for producing a photocatalytic powder material or slurry which can satisfy all of the photocatalytic activity, when used in combination with an organic material, durability and dispersion stability.
In view of these conventional techniques, an object of the present invention is to provide a photocatalytic powder material, a slurry containing the photocatalytic powder, an organic polymer composition containing the photocatalytic powder, a molded article of the organic polymer composition, a coating agent containing the slurry and a structure having provided on the surface thereof the organic polymer composition or the coating agent that can effectively and profitably perform removal of malodor, decompositional removal of harmful substances or pollutants in air, water draining or cleaning treatment, or disinfectant or antifungal action (hereinafter collectively called xe2x80x9cenvironmental cleaning activityxe2x80x9d) and at the same time, have high dispersion stability, and therefore, be greatly enhanced in the industrial utility.
Particularly, the present invention provides a photocatalytic powder and a photocatalytic slurry, which can exhibit excellent photocatalytic activity, durability and dispersion stability when coated on the surface of fiber, paper or plastic material, kneaded into such a material, or used for a coating composition.
As a result of extensive investigations to attain the above-described objects, the present inventors have found that these objects can be attained by a photocatalytic powder material comprising a titanium dioxide fine particle containing an anionically active substance, wherein the electrokinetic potential of the fine particle is from about xe2x88x92100 to 0 mV in an aqueous environment at pH 5, and by a slurry containing the powder.
More specifically, the present invention provides the following embodiments.
(1) A photocatalytic powder comprising a titanium dioxide fine particles containing an anionically active substance, wherein the electrokinetic potential of the fine particle is from about xe2x88x92100 to 0 mV in an aqueous environment at pH 5.
(2) The photocatalytic powder as described in 1 above, wherein the fine particle has a primary particle size of about 0.001 to about 0.2 xcexcm.
(3) The photocatalytic powder as described in 1 or 2 above, wherein the anionically active substance is at least one substance selected from the group consisting of condensed phosphoric acid, organic sulfonic acid, sulfuric acid and hydrofluoric acid.
(4) An aqueous slurry containing the photocatalytic powder described in any one of 1 to 3 above.
(5) An organic polymer composition containing the photocatalytic powder described in any one of 1 to 3 above.
(6) A coating agent using the photocatalytic slurry described in 4 above.
(7) An organic polymer composition comprising the photocatalytic powder described in 5 above, wherein the organic polymer of the organic polymer composition is at least one selected from the group consisting of thermoplastic resin, thermosetting resin, synthetic resin, natural resin and hydrophilic polymer.
(8) An organic polymer composition comprising the photocatalytic powder described in 5 above, wherein the organic polymer composition is an article selected from the group consisting of a coating material, a coating composition, a compound and a masterbatch.
(9) The organic polymer composition containing a photocatalytic powder as described in 8 above, wherein the concentration of the photocatalytic powder in the organic polymer composition is from about 0.01 to about 80% by mass based on the entire mass of the composition.
(10) A photocatalytic functional molded article obtainable by molding the organic polymer composition containing a photocatalytic powder material described in any one of 7 to 9 above.
(11) The photocatalytic functional molded article as described in 10 above, which is a molded article selected from the group consisting of fiber, film and plastic.
(12) A photocatalytic functional structure having provided on the surface thereof the photocatalytic powder described in any one of 1 to 3 above.
(13) A photocatalytic functional structure having provided on the surface thereof the coating agent described in 6 above.
(14) A coating layer comprising the photocatalytic powder described in 1 or 2 above.
The titanium dioxide for use in the present invention is fundamentally not limited in the crystal form or in the production process thereof as long as it has photocatalytic activity. For example, a titanium dioxide fine particle obtained by a vapor phase reaction starting from titanium halide, a titanium dioxide fine particle or sol obtained by wet-hydrolyzing a titanium halide solution, or a calcined product thereof, may be used.
The titanium dioxide fine particle for use in the present invention is not limited in the crystal form, as described above. However, from the viewpoint of attaining high performance as a photocatalyst, anatase and brookite are preferred. The titanium dioxide fine particle may also be a composite crystal-system fine particle of these crystal forms or containing such a crystal.
The titanium dioxide for use in the present invention preferably has an average primary particle size of about 0.001 to about 0.2 xcexcm, more preferably from about 0.001 to about 0.1 xcexcm. If the average primary particle size is less than about 0.001 xcexcm, efficient production is difficult to attain and this is not practical, whereas if it exceeds about 0.2 xcexcm, the photocatalytic performance of the titanium dioxide greatly decreases.
In the present invention, it is important that the fine powder mainly comprises the above-described titanium dioxide, that the titanium dioxide contains an anionically active substance and that the electrokinetic potential of the fine powder is from about xe2x88x92100 to 0 mV in an aqueous environment at pH 5. The term xe2x80x9cmainlyxe2x80x9d used herein means more than 50%. The xe2x80x9canionically active substancexe2x80x9d as used herein means a substance having a hydrophilic atom group showing anionic property in the molecule, the surface of which substance is readily rendered anionic in water due to its proton-donating property. Any substance satisfying these conditions may be used. For example, the substance having a hydrophilic atom group bearing an anion in the molecule (particularly, Bronsted acid) is at least one substance selected from the group consisting of condensed phosphoric acid, organic sulfonic acid, sulfuric acid and hydrofluoric acid. Examples of the condensed phosphoric acid include pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid and hexametaphosphoric acid. Examples of the organic sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid and dodecylbenzenesulfonic acid. Among these, condensed phosphoric acid is preferred.
In the present invention, an anionically active substance compounded with titanium dioxide is present in the vicinity of the surface of a fine particle, an anionically substance is adsorbed to the surface of a titanium dioxide fine particle, or an anionically active substance is present in the vicinity of the surface of titanium dioxide. The powder material may be in any of these states.
In the present invention, the electrokinetic potential means a potential difference generated at the interface between a solid particle and water in contact with each other when they perform a relative motion. This electrokinetic potential is generally determined, for example, by a method of loading an electric field to both ends of a cell containing water having dispersed therein fine powder to cause electrophoresis and measuring the migration speed. For the measurement of the migration speed, a direct observation method through a microscope, a rotary prism method, a laser Doppler method, a laser rotary grating method, an image analysis method or a mass measuring method may be used.
Other than the electrophoresis method, a precipitation potential method, an electroosmosis method, a streaming potential method and an ultrasonic method may be used. Among these, an electrophoretic light-scattering method is preferred, which is an electrophoresis method employing a laser Doppler speed measuring method. In the present invention, the electrokinetic potential at pH 5 must be from about xe2x88x92100 to 0 mV, preferably from about xe2x88x9250 to about xe2x88x9210 mV. If the electrokinetic potential value exceeds about 0, sufficiently high photocatalytic activity cannot be obtained and also, the dispersion stability is poor, whereas if the electrokinetic potential is less than about xe2x88x92100 mV, sufficiently high photocatalytic activity cannot be obtained.
In the present invention, the anionically active substance may be sufficient if it is present in a ratio based on titanium dioxide such that the electrokinetic potential of the fine particle is from about xe2x88x92100 to 0 mV in an aqueous environment at pH 5. For example, the anionically active substance is preferably in a ratio of about 0.1 to about 50 parts by mass, more preferably from about 0.2 to about 20 parts by mass, per about 100 parts by mass of titanium dioxide. If the ratio of the anionically active substance is less than about 0.1 part by mass, sufficiently high dispersion stability of the fine particle cannot be obtained, whereas if it exceeds about 50 parts by mass, the fine particle greatly decreases in the activity as a photocatalyst. The method for allowing the anionically active substance to be present on the surface of titanium dioxide is also not particularly limited. For example, the anionically active substance may be added in the initial stage or during the production of titanium dioxide, or the anionically active substance may be added in the surface treatment step after the completion of the production of titanium dioxide.
In the photocatalytic powder, a metal such as platinum, rhodium, ruthenium, palladium, silver, copper and zinc may be previously supported on the surface of a titanium dioxide fine particle. In this case, the titanium dioxide fine particle is more intensified in the environmental cleaning activity and the disinfectant or algicidal effect is also enhanced. The metal may also be supported on the raw material titanium dioxide or a step of allowing the metal to be supported may be provided in the process of incorporating the above-described anionically active substance.
The slurry of the present invention is an aqueous dispersion comprising a photocatalytic powder material which is a fine particle mainly comprising a titanium dioxide fine particle and further containing an anionically active substance and in which the electrokinetic potential of the fine particle is from about xe2x88x92100 to 0 mV in an aqueous environment at pH 5. A hydrophilic organic solvent may be added to this aqueous dispersion.
The content ratio of the photocatalytic powder in the slurry is not particularly limited but is preferably, for example, from about 0.01 to about 50% by mass, more preferably from about 1 to about 40% by mass. If the content of the photocatalytic powder is less than about 0.01% by mass, a sufficiently high photocatalytic effect may not be obtained after the coating, whereas if it exceeds about 50% by mass, not only a problem such as increase in viscosity may be caused, but also is disadvantageous in view of profitability.
A photocatalytic functional structure may be produced by adding a freely selected binder to the above-described aqueous dispersion (slurry) to form a coating agent and coating such aqueous dispersion on the surface of various structures, which are described later. In the present invention, the binder material is not limited but, for example, at least one selected from hydrophilic polymers, such as polyvinyl alcohol, sodium polyacrylate and poly(N-vinylacetamide), and inorganic materials, such as zirconium compound, may be used.
Examples of the zirconium compound include zirconium oxychloride, zirconium hydroxychloride, zirconium nitrate, zirconium sulfate, zirconium acetate, ammonium zirconium carbonate and zirconium propionate.
Specifically, the amount of the binder added to the coating agent is preferably, for example, from about 0.01 to about 20% by mass, more preferably from about 1 to about 10% by mass. If the content of the binder is less than about 0.01% by mass, sufficiently high adhesion may not be attained after the coating, whereas if it exceeds about 20% by mass, not only a problem, such as increase in viscosity, may be caused, but also is disadvantageous in view of profitability.
The photocatalytic powder of the present invention can be used as a composition by adding it to an organic polymer. The organic polymer which can be used here includes thermoplastic resin, thermosetting resin, synthetic resin, natural resin and hydrophilic polymer. By incorporating the above-described anionically active substance to the titanium dioxide, the occurrence of the organic polymer directly contacting the active face (surface) of the photocatalyst is reduced, and therefore, the organic polymer substrate itself is scarcely subject to decompositional deterioration.
Examples of this organic polymer include polyethylene, nylon 6, nylon 66, polyvinyl chloride, polyvinylidene chloride, polyester, polypropylene, polyethylene oxide, polyethylene glycol, polyethylene terephthalate, silicon resin, polyvinyl alcohol, vinyl acetal resin, polyacetate, ABS resin, epoxy resin, vinyl acetate resin, cellulose, cellulose derivatives, polyamide resin, polyurethane resin, polycarbonate resin, polystyrene rein, urea resin, fluororesin, polyvinylidene fluoride, phenol resin, celluloid, chitin, starch sheet, acrylic resin, unsaturated polyester, melamine resin, alkyd resin and rayon.
The organic polymer composition containing the photocatalytic powder for environmental cleaning of the present invention can be used in the form of a coating material, a coating composition, a compound or a masterbatch. The concentration of the photocatalyst in the organic polymer composition is from about 0.01 to about 80% by mass, preferably from about 1 to about 50% by mass, based on the entire mass of the composition. In this polymer composition, an absorbent such as activated carbon and zeolite may be added to enhance the effect of removing malodorous substances. In the present invention, a polymer molded article having a function of cleaning the environment can be obtained by molding the above-described polymer composition. Examples of the molded article of the composition include fiber, film and plastic molded article.
The polymer composition of the present invention has excellent durability and therefore, may also be used as a coating composition for a structure such as wall material, glass, billboard or road construction concrete. Furthermore, when the titanium dioxide or polymer composition of the present invention is subjected to a surface treatment, its photocatalytic function can be fully exhibited without causing any photocatalytic deterioration or destruction of the medium (structure or coating), even if coated on a structure (organic material), such as paper, plastic, cloth or wood, or on a body coating of a car or the like.